Differential gear device for vehicle

ABSTRACT

An internal gear  4  and a sun gear  5  are arranged on one end side and the other end side within a housing  1  which is driven for rotation about a rotation axis L. The internal gear  4  and the sun gear  5  are rotatably disposed about the rotation axis L. A first gear part  61  and a second gear part  62,  which are different from each other in number of teeth, are formed on one end part and the other end part of a planetary gear  6,  respectively. The first gear part  61  is meshed with an internal gear part  42  of the internal gear  4.  The second gear part  62  is meshed with an external gear part  51  of the sun gear  5.

TECHNICAL FIELD

This invention relates to a differential gear apparatus for vehicles inwhich a planetary gear mechanism is utilized.

BACKGROUND ART

In general, a differential gear apparatus of this type comprises aninternal gear and a sun gear rotatably arranged with their axes alignedwith each other, a carrier rotatably arranged with its axis aligned withthe axes of the internal gear and the sun gear, and a planetary gearrotatably (rotatably about its own axis) supported by the carrier andmeshed with the internal gear and the sun gear. When the carrier isdriven for rotation, its rotation is transmitted to the internal gearand the sun gear through the planetary gear. When the planetary gear isnot rotated about its own axis, the internal gear and the sun gear areintegrally rotated together at the same rotational speed and withoutbeing rotated relative to each other. On the other hand, when theplanetary gear is rotated about its own axis, the internal gear and thesun gear are differentially rotated in accordance with rotational speedof the planetary gear (see Official Gazette of Japanese PatentApplication Laid-Open No. H09-112657).

In the above-mentioned conventional differential gear apparatus, thereis such a problem that when the respective pitch circle diameters of theinternal gear and the sun gear are determined, the ratio of rotationtorques (torque bias ratio) transmitted to the internal gear and the sungear is primarily determined and the ratio is unchangeable. For example,in case the respective circle pitch diameters of the internal gear andthe sun gear are represented by D1, D2, respectively, the torque biasratios are primarily determined as D1:D2.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided, in order to solvethe above-mentioned problem, a differential gear apparatus for vehiclescomprising an internal gear which is rotatably disposed, a sun gearwhich is rotatably disposed with an axis thereof aligned with that ofthe internal gear, and a planetary gear disposed between the internalgear and the sun gear such that the planetary gear can rotate about itsown axis and can revolve, wherein the planetary gear is provided with afirst and a second gear part which are different in pitch circlediameter, the first gear part is meshed with the internal gear, and thesecond gear part is meshed with the sun gear.

The pitch circle diameter of the first gear part may be larger orsmaller than that of the second gear part.

If a pitch circle diameter of the internal gear is represented by D1, apitch circle diameter of the sun gear, by D2, and a pitch circlediameters of the first and second gear parts of the planetary gear, byD3, D4, respectively, either D1/D3≧D2/D4 or D1/D3<D2/D4 can beestablished with respect to D1 through D4.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view taken on line X-X of FIG. 2, showing oneembodiment of the present invention.

FIG. 2 is a sectional view taken on line X-X of FIG. 1.

FIG. 3 is a sectional view taken on line Y-Y of FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of the present invention will be described hereinafterwith reference to FIGS. 1 through 3.

A differential gear apparatus 1 for vehicles according to thisembodiment is used, for example, as a center differential gear andmainly comprises, as shown in FIG. 1, a housing 2, a carrier 3, aninternal gear 4, a sun gear 5 and a planetary gear 6.

The housing 2 is driven for rotation about a rotation axis L andincludes a circular cylindrical main body part 21 with its axis alignedwith the rotation axis L. A bottom part 22 is formed on one end part(left end part of FIG. 1) of this main body part 21. A bearing part 23with its axis aligned with the rotation axis L is formed on the outerside end face of the bottom part 22. A carrier 3 is received in theother end part of the main body part 21. This carrier 3 is non-rotatablyconnected to the other end part of the main body part 21 by splinefitting and tightly fastened by fastening means which is threadinglyengaged with the inner peripheral surface of the main body part 21, sothat the carrier 3 is non-movable in the direction of the rotation axisL. First and second output shafts (not shown) are rotatably thrust inthe inner peripheral surfaces of the bearing part 23 and the carrier 3,respectively. The housing 2 is rotatably supported by those first andsecond output shafts about the rotation axis L.

The internal gear 4 is rotatably arranged on the bottom part 22 sidewithin the main body part 21 with its axis aligned with the rotationaxis L. An annular protrusion 41 protruding radially inward is formed onone end part (end part on the bottom part 22 side) of the innerperipheral surface of the internal gear 4. A circular cylindricalintermediate member 72 is non-rotatably connected to the innerperipheral surface of the annular protrusion 41 by spline fitting or thelike. The annular protrusion 41 and the intermediate member 72 areconnected to the bottom part 22 through a washer 73. One end part of thefirst output shaft is non-rotatably connected to the inner peripheralsurface of the intermediate member 72 through spline fitting or thelike. The other end part of the first output shaft is connected to, forexample, a rear differential gear (not shown). An internal gear part 42having a helical tooth is formed on the other end face of the innerperipheral surface of the internal gear 4.

The sun gear 5 is rotatably arranged on the carrier 3 side within themain body part 21 with its axis aligned with the rotation axis L. Oneend face (left end face in FIG. 1) of the sun gear 5 is in contact withthe intermediate member 72 through a washer 74 and further in contactwith the bottom part 22 through the intermediate member 72 and thewasher 73. The other end face of the sun gear 5 is in contact with thecarrier 3 through a washer 75. Accordingly, the sun gear 5 is almostnon-movably in the direction of the rotation axis L. An external gearpart 51 having a helical tooth is formed on the outer peripheral surfaceof the sun gear 5. This external gear part 51 is same in gearspecifications such as module, pressure angle, helical angle, etc. asthe internal gear part 42 excepting the number of teeth and the helicaldirection. The number of teeth of the external gear part 51 is smallerthan the number of teeth of the internal gear part 42. Accordingly, theoutside diameter of the external gear part 5 is smaller than the insidediameter of the internal gear part 42. One end part of the second outputshaft is non-rotatably connected to the inner peripheral surface of thesun gear 5 by spline fitting or the like. The other end part of thesecond output shaft is connected to, for example, a front differentialgear (not shown).

A circular cylindrical supporting part 31 is formed on the end face onthe bottom part 22 side of the carrier 3. This supporting part 31 isdisposed with its axis aligned with the rotation axis L. A plurality(six in this embodiment) of first receiving holes 32 extending parallelto the rotation axis L are arranged on the forward end face of thesupporting part 31 at equal intervals in the peripheral direction of thesupporting part 31. As shown in FIG. 2, the inside diameter of eachfirst receiving hole 32 is set to be larger than the thickness of thesupporting part 31, and the side parts on the outer side and the innerside of the first receiving hole 32 in the radial direction of thesupporting part 31 are open to outside at the outer peripheral surfaceand the inner peripheral surface of the supporting part 31,respectively. The first supporting hole 32 extends from the forward endface of the supporting part 31 to an intermediate part of the supportingpart 31. A second receiving hole 33 is formed in a bottom part of thefirst receiving hole 32 with its axis aligned with that of the firstreceiving hole 32. The inside diameter of the second receiving hole 33is set to be smaller than that of the first receiving hole 32. As shownin FIG. 3, the side part of the second receiving hole 33 on the radiallyinner side of the supporting part 31 is open to outside at the innerperipheral surface of the supporting part 31.

A first gear part 61 is formed on one end part (left end part of FIG. 1)of the planetary gear 6 and a second gear part 62 is formed on the otherend part. The first gear part 61 is rotatably fitted to the firstreceiving hole 32 and meshed with the internal gear part 42 of theinternal gear 4 at the outer side opening part of the first receivinghole 32. The second gear part 62 is rotatably fitted to the secondreceiving hole 33 and meshed with the external gear part 51 of the sungear 5 at the inner side opening part of the second receiving hole 33.Owing to this arrangement, when the housing 2 is driven for rotation,its rotation is transmitted to the planetary gear 6 through the carrier3 and transmitted further to the internal gear 4 and the sun gear 5 fromthe planetary gear 6. When the planetary gear 6 is not rotated about itsown axis, the internal gear 4 and the sun gear 5 are integrally rotatedat the same rotational speed. On the other hand, when the planetary gear6 is rotated about its own axis, the internal gear 4 and the sun gear 5are rotated differentially in according with the rotational speed of theplanetary gear 6.

As apparent from a fact that the first gear part 61 and the second gearpart 62 are meshed with the internal gear part 42 and the external gearpart 51, respectively, the first and second gear parts 61, 62 have thesame gear specifications except that their number of teeth is differentand their helical direction is different. The number of teeth of thefirst gear part 61 is larger than the number of teeth of the second gearpart 62. If the numbers of teeth of the internal gear part 42, theexternal gear part 51, the first gear part 61 and the second gear part62 are represented by N1, N2, N3 and N4, respectively, the followingformula can be obtained.N1>N2, N3>N4and the numbers N1 through N4 of teeth are determined so that thefollowing equation can be established.N 1/N 3=N 2/N 4Moreover, since the gear parts 42, 51, 61, 62 are same in module andhelical angle, if the pitch circle diameter (meshing pitch circlediameter with respect to the internal gear part 42) of the internal gearpart 42 is represented by D1, the pitch circle diameter (meshing pitchcircle diameter with respect to the second gear part 62) of the externalgear part 51, by D2, the pitch circle diameter (meshing pitch circlediameter with respect to the internal gear part 42) of the first gearpart 61, by D3, and the pitch circle diameter (meshing pitch circlediameter with respect to the eternal gear part 51) of the second gearpart 62, by D4, respectively, the following formula can be established.D1>D2, D3>D4D 1/D 3=D 2/D 4Thus, in this differential gear apparatus 1, the torque bias ratio as aratio between the rotation torque transmitted to the internal gear 4 andthe rotation torque transmitted to the sun gear 5 is 50:50. That is,rotation torques having the same magnitude are transmitted to theinternal gear 4 and the sun gear 5, respectively.

The respective pitch circle diameters D1, D2, D3 and D4 of the internalgear part 42, the external gear part 51, the first gear part 61 and thesecond gear part 62 can also be set such that the following formula canbe established.D 1/D 3>D 2/D 4They can also be set such that the following formula can be established.D 1/D 3<D 2/D 4In the former case, the rotation torque transmitted to the internal gear4 is larger than the rotation torque transmitted to the sun gear 5. Inthe latter case, the rotation torque transmitted to the internal gear 4is smaller than the rotation torque transmitted to the sun gear 5.

Since the first and second gear parts 61, 62 are opposite to each otherin helical direction, the acting direction of the thrust force generatedin the planetary gear 6 due to meshing engagement between the internalgear part 42 and the first gear part 61 is equal to the acting directionof the thrust force generated in the planetary gear 6 due to meshingengagement between the external gear part 51 and the second gear part62. In this embodiment, the helical directions of the first and secondgear parts 61, 62 are determined such that when the housing 2 is drivenfor rotation in such a manner as to advance the vehicle, the left endface of the planetary gear 6 is pressed against the bottom part 22 bythe thrust force acting on the planetary gear 6, through the washer 76,the annular protrusion 41 of the internal gear 4 and the washer 73. Ofcourse, conversely, the helical directions of the first and second gearparts 61, 52 may be determined such that a thrust force for pressing theplanetary gear 6 against the carrier 3 is generated. In that case, theright end face of the planetary gear 6 is preferably contacted with thecarrier 3 through a washer (not shown).

In the differential gear apparatus 1 thus constructed, since theplanetary gear 6 is provided with the first gear part 61 and the secondgear part 62 which are mutually different two gears and those first andsecond gear parts 61, 62 are meshed with the internal gear 4 and the sungear 5, respectively, the torque bias ratio can be selectedcomparatively freely by appropriately selecting the respective pitchcircle diameters.

Moreover, in the differential gear apparatus 1 of this embodiment, sincethe helical directions of the first gear part 61 and the second gearpart 62 are opposite to each other, the acting direction of the thrustforce generated due to meshing engagement between the first gear part 61and the internal gear 4 is same as the acting direction of the thrustforce generated due to meshing engagement between the second gear part62 and the sun gear 5. As a result, the planetary gear 6 is axiallypushed by a large force, the left end face of the planetary gear 6 ispressed against the annular protrusion 41 of the internal gear 4 throughthe washer 76 and further pressed against the bottom part 22 of thehousing 2 through the annular protrusion 41 and the washer 73. Thus,during the differential operation, large friction resistance isgenerated between the planetary gear 6 and the internal gear 4 andbetween the internal gear 4 and the housing 2. By this, the differentialrotation can be restricted. In case the first gear part and the secondgear part are same in helical direction, the acting direction of thethrust force generated in the first gear part 61 and the actingdirection of the thrust force generated in the second gear part 62 areopposite to each other. Therefore, two thrust forces are offset. As aresult, only the small thrust force remained after the offset would acton the planetary gear 6 and therefore, the differential operationrestricting performance would be reduced.

The present invention is not limited to the above-mentioned embodiment,and many changes and modifications can be made in accordance withnecessity.

For example, in the above-mentioned embodiment, the first and secondgear parts 61, 62 are same in gear specifications excepting the numberof teeth and the helical direction, and as a result, the pitch circlediameter D3 of the first gear part 61 having a larger number of teeth islarger than the pitch circle diameter of the second gear part 62.However, for example, by making the first and second gear partsdifferent in module, it is possible to make the pitch circle diameter ofthe first gear part 61 same as the pitch circle diameter of the secondgear part 62, while satisfying the conditions of D1/D3>D2/D4 orD1/D3<D2/D4.

Industrial Applicability

A differential gear apparatus for vehicles according to the presentinvention can be used a front differential gear or rear differentialgear for automobiles, or as a center differential gear for four-wheeldrive vehicles.

1. A differential gear apparatus for vehicles comprising an internal gear which is rotatably disposed, a sun gear which is rotatably disposed with an axis thereof aligned with that of said internal gear, and a planetary gear disposed between said internal gear and said sun gear such that said planetary gear can rotate about its own axis and can revolve, wherein said planetary gear is provided with a first and a second gear part which are different in pitch circle diameter, said first gear part is meshed with said internal gear, and said second gear part is meshed with said sun gear.
 2. A differential gear apparatus for vehicles according to claim 1, wherein if a pitch circle diameter of said internal gear is represented by D1, a pitch circle diameter of said sun gear, by D2, and a pitch circle diameters of said first and second gear parts of said planetary gear, by D3, D4, respectively, D1/D3≧D2/D4 can be established.
 3. A differential gear apparatus for vehicles according to claim 1, wherein if a pitch circle diameter of said internal gear is represented by D1, a pitch circle diameter of said sun gear, by D2, and a pitch circle diameters of said first and second gear parts of said planetary gear, by D3, D4, respectively, D1/D3<D2/D4 can be established.
 4. A differential gear apparatus for vehicles according to claim 1, wherein said first gear part is larger than said second gear part in pitch circle diameter.
 5. A differential gear apparatus for vehicles according to claim 4, wherein if a pitch circle diameter of said internal gear is represented by D1, a pitch circle diameter of said sun gear, by D2, and a pitch circle diameters of said first and second gear parts of said planetary gear, by D3, D4, respectively, D1/D3>D2/D4 can be established.
 6. A differential gear apparatus for vehicles according to claim 4, wherein if a pitch circle diameter of said internal gear is represented by D1, a pitch circle diameter of said sun gear, by D2, and a pitch circle diameters of said first and second gear parts of said planetary gear, by D3, D4, respectively, D1/D3<D2/D4 can be established.
 7. A differential gear apparatus for vehicles according to claim 1, wherein said first gear part is smaller than said second gear part in pitch circle diameter.
 8. A differential gear apparatus for vehicles according to claim 7, wherein if a pitch circle diameter of said internal gear is represented by D1, a pitch circle diameter of said sun gear, by D2, and a pitch circle diameters of said first and second gear parts of said planetary gear, by D3, D4, respectively, D1/D3>D2/D4 can be established.
 9. A differential gear apparatus for vehicles according to claim 7, wherein if a pitch circle diameter of said internal gear is represented by D1, a pitch circle diameter of said sun gear, by D2, and a pitch circle diameters of said first and second gear parts of said planetary gear, by D3, D4, respectively, D1/D3<D2/D4 can be established. 